Arc tube mount



Dec. 22, 1959 J. M. POMFRETT E'ITAL 2,918,592

ARC TUBE MOUNT Filed June 25, 1958 lnven tovs: John M. pom f've t k,

Fvahk define dri, 8

United States Patenf ARC TUBE MOUNT John M. Pomfrett, Willoughby, and Frank Jenne, Jr., Euclid, Ohio, assignors to General Electric Company,

a corporation of New York Application June 23, 1958, Serial No. 743,572

8 Claims. Cl. 313-25 This invention relates to electric discharge lamps of the high pressure mercury vapor discharge type having an arc tube mounted in a vitreous outer envelope or jacket. The invention is more particularly concerned with the mount or structure for supportingthe arc tube within the jacket.

Mercury vapor lamps in sizes ranging from 85 to 1000 watts generally comprise a relatively soft glass outer jacket having a screw base at one end and enclosing a generally cylindrical high pressure are tube. The jacket keeps air away from the arc tube, seals and provides mechanical protection while serving also as a heat conservator and short wave ultraviolet filter. The are tube maybe made of hard or quartz-like glass but is now more commonly made of quartz. It contains a quantity of mercury along with'a starting gas and is provided with thermionic self-heating electrodes. An auxiliary starting electrode is generally located at one end of the arc tube and is connected through a current limiting resistor to the main electrode at the opposite end. The space between the arc tube and the outer envelope or jacket may be either evacuated or filled with an inert gas such as nitrogen.

The advent of quartz are tubes having their ends closed by full diameter pinch seals has presented new problems in regards to mounting the arc tube within the jacket. A mounting structure has been desired which is easy and economical to manufacture, which does not interfere with the efficient operation of the arc tube, and which preferably absorbs only the very least quantity of light therefrom.

Accordingly the object of the invention is to provide a new and improved mount for the arc tube in the jacket of a high pressure lamp.

A more specific object is to provide a mount structure, for a quartz arc tube having full diameter pinch seals, which causes minimal absorption of light in the lamp and which is at the same time rugged and economical to manufacture.

In accordance with the invention, the arc tube is supported and held in place within the jacket principally by a single support rod which is fastened at its stem end to one of the lead-in wires projecting through the stem of the jacket. In a preferred embodiment, the rod extends the length of the jacket and is fixed in place at its other end by means of spring fingers contacting the wall of the jacket at its outer end. The are tube is fastened to this single support rod by means of a pair of straps wrapped around the pinch seals which are provided with suitable locking portions inter-engaging the straps to prevent axial displacement of the arc tube. The straps engage the pinch seals at some distance from the arc chamber in order to avoid electrolysis of the quartz which would occur were the straps allowed to contact the hot 'quartz, of the wall of the arc chamber. The single support rod serves simultaneously as a current conductor to the electrode situated at the remote end of the arc tube. In a preferred construction, the stem end of the arc tube is provided with an integral support lead connected within the pinch seal to the foil section of an electrode inlead and fastened at its other end to one of the lead wires projecting inwardly through the stem of the jacket.

For further objects and advantages and for a detailed description of the invention, attention is now directed to the following description and accompanying drawing illustrating embodiments of the invention. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawings:

Fig. 1 is a front elevation view of a high pressure mercury vapor lamp embodying the invention with the front portion of the outer jacket cut away to expose the arc tube and the mount therefor.

Fig. 2 is a sectional view through the upper end of the lamp of Fig. 1.

Fig. 3 is a detail showing the strap and the locking ridge on the pinch seal engaging it.

Fig. 4 is a detail of a modified construction showing the strap and the flared end of the pinch engaging same.

Fig. 5 is a detail of another modified construction using a dent in the pinch seal to lock with the strap.

Referring to the drawing and more particularly to Fig. 1, there is shown a high pressure mercury vapor lamp 1 comprising an outer vitreous envelope or jacket 2 of generally tubular form modified by a central bulbous portion 3. The bulbous form reduces the temperature of the envelope in the immediate vicinity of the arc tube where it tends to be highest. The jacket is provided at its lower end with a re-entrant stem 4 having a press 5 through which extend relatively stiff inlead wires 6, 7 connected at their outer ends to the contacts of the usual screw-type base 8, namely the threaded shell 9 and the insulated center contact 11.

The inner arc tube 12 is made of quartz and has sealed therein at opposite ends a pair of main discharge supporting electrodes 13, 14 supported on inleads 15, 16 which constitute the arc tube terminals. Each main electrode comprises a core portion which may be a prolongation of the inner end of the inlead made of a suitable refractory metal such as tungsten or molybdenum, and surrounded by a tungsten wire helix 17. A small elongated piece or sliver of thorium metal (not shown in the draw; ing) is inserted between the core and the helix and serves to reduce the cathode drop at the electrodes during operation. An auxiliary starting electrode 18 is provided at the base end of the arc tube adjacent main electrode 13 and consists merely of the inwardly projecting end of the inlead.

Current inleads 15, 16 and 18 have their ends welded to intermediate foil sections 19 of molybdenum hermetically sealed within quartz pinch seal portions 21, 22. The foil sections are very thin, for instance approximately .0008" thick and go into tension when the quartz cools without rupturing or shaling off from the quartz. Relatively short molybdenum wire sections 23, 24 are welded to the outer ends of the foils in the case of inleads 16 and 18. These have substantially nomechanical support function and serve merely as electrical connectors. Inlead wire 23 is electrically connected to single support rod 25 by a resistor 26 welded thereto. This resistor may have a value for instance of 40,000 ohms and serves to limit the current to auxiliary electrode 18 during normal operation of the lamp. Inlead wire 24 is connected to the reverted end 25a of transversely directed portion 25b of support wire 25 by a flexible wire 28 whereby to energize main electrode 14. 1

A longer inlead wire 30 is provided for main electrode 13 at the stem or base end of the arc tube because it has a mechanical support function in addition to its current carrying function. Wire 30 is welded at one Patented Dec. 22, 1959 i end to the bent over portion of stem lead-in wire 7. Its other end enters pinch seal 21 through a funnel-like opening 31 near its edge and is bent over at right angles immediately beyond the apex of the opening and is welded to the outer end of foil 19 of inlead 15. The funnel or bell-like opening 31 through which inlead 3i) emerges from the pinch seal isdesirable in order to prevent cracking of the corner'of the pinch seal.

The pinched or flattened end portions 21, 22 of the arc tube form wide seals using substantially the full diameter of the tube. They are made by flattening or compressing the ends of the arc tube without prior necking down to a smaller diameter. This may be achieved by following the teachings of copending application Serial No. 607,005, filed August 30, 1956, of Klaus Gottschalk, entitled Quartz Tube Pinch Seal and assigned to the same assignee as the present invention. The arc tube is provided with a filling of an ionizable medium consisting of a supply of mercury in sufficient quantity to be completely vaporized with a pressure of the order of /2 to several atmospheres during operating of the lamp. In addition a small quantity of a rare gas such as argon at a low pressure, for instance at approximately 25 millimeters pressure, is provided to facilitate starting.

The principal support of the arc tube is provided by longitudinally extending side rod 25 whose base end is welded to the laterally bent over portion of lead-in wire 6. An intermediate portion 250 of the rod is laterally offset for reducing the heating thereof and shadow effect by placing it at a greater distance from the arc tube. The upper laterally directed end portion 25b of the support rod is fixed in place by transverse spring members 33, 34 whose ends bear against the tubular outer end of the jacket. A heat reflector disc 35 is mounted transversely to the axis of the envelope at the stem orbase end and is welded to main lead-in wire 7 while support rod 25 passes through a slot 36 therein without any contact.

The are tube is clamped to the support rod by means of a pair of straps 37, 37'. As best seen in Fig. -3, strap 37 is channel-shaped on one side 37a and fiat on the other side 37b; the fiat portion is bent to conform to the outline of the pinch seal. The channel and fiat portions are welded together at the wrap-around point and the channel portion is welded to the support rod.

In accordance with an important feature of the invention, at least strap 37 at the base end of the arc tube is spaced an appreciable distance from the wall of the arc chamber. This is desirable in order to avoid devitrification of the end of the arc tube about inlead 15. Such devitrification would be apt to occur due to the fact that strap 37 is connected into the electrical circuit of main electrode 14 and is therefore at a potential difference equal to the arc tube drop from the potential of main electrode 13. For the sake of symmetry, and also in order to prevent excessive cooling of the ends of the arc tube causing excessively long warm-up time, both straps 37 and 37 are spaced from the ends of the arc chamber. In order to prevent axial movement of the arc tube relative to the straps, locking portions consisting of transverse ridges 38 are formed across the faces of the pinch seals which are engaged by straps 37, 37'. The edges of the fiat portions 37b of the straps bear against the ridges so that the arc tube is locked against lateral displacement.

In the embodiment of the invention illustrated in Fig. 4, the arc tube is locked against axial displacement by resting the outer edge of strap 37 against conical aperture 31 and the outer edge of strap 37 against a similar dummy conical aperture 31. formed at the outer end of the arc tube.

In the embodiment of the invention illustrated in Fig. 5, the arc tube is locked against axial displacement by providing small cavities or dents in the quartz of the pinch seal under straps 37, 37. The straps are pro- 4 vided with corresponding internal bosses or depressions 39 which engages the dents in the quartz and thereby lock the arc tube to the straps.

The single support rod mount structure which has been described has the advantages of low cost and ease of manufacture. A conductor extending the length of the arc tube is necessary in order to provide current connections to the electrode at the outer end of the arc tube. The present construction combines therewith the function of mechanical support. The problem of sagging of this conductor, which might otherwise by encountered in a horizontally mounted lamp when a slender wire is used therefor, is avoided. At the same time the cost of the inleads to the arc tube, which are .of molybdenum and therefore relatively expensive, is kept down by using only small molybdenum inlead wires 23 and 24 for auxiliary electrode 18 and main electrode 14. In the case of main electrode 13, a longer molybdenum inlead wire 30 is used but it combines with its function of conductor that .of mechanical support of the arc tube and particularly prevents axial turning or twisting ,of the arc tube within the jacket. The overall result is anarc tube mount fully adequate in strength and rigidity and lowest in combined cost of component parts and manufacture.

While the invention has been described by reference to specific preferred embodiments of same in a given size of lamp, these including the details of construction are intended as exemplary and not in order to limit the invention thereto except in so far as included in the appended claims.

What we claim as new and desire to secure byLLetters Patent of the United States is:

1. An electric discharge lamp comprising a vitreous outer jacket enclosing a generally cylindrical arc tube closed by full diameter pinch seals defining an arc chamber having electrodes sealed therein at-OPPOsite ends, a stern closing an end of said jacket and having a pair of lead-in wires projecting therethrough, a single support rod fastened to one of said lead-in wires and extending through the jacket, a pair of metal straps wrapped around the pinch seals of the are tube at points removed from the ends of the arc chamber and fastened to said support rod, and locking portions on said pinch seals inter-engaging the straps to prevent axial displacement of the arc tube.

2. An electric discharge lamp comprising a vitreous outer jacket enclosing a generally cylindrical arc tube closed by full diameter pinch seals defining an arc chamber having electrodes sealed therein at opposite ends, a stern closing an end of said jacket andghaving-a pair of lead-in wires projecting therethrough, ,,a single support rod fastened to one of said lead-in wires and extending through the jacket, a pair of metal straps wrapped around the pinch seals of the arc tube at points removed from the ends of the arc chamber and fastened to said support rod, and an inlead embedded in the pinch seal at the stem end of the are tube providing a .connection to the electrode and fastened to the other of said lead-in wires.

3. An electric discharge lamp comprising a vitreous outer jacket enclosing a generally cylindrical arc tube closed by full diameterpinch seals defining an arc chamber having electrodes sealed therein at opposite .ends,. a stem closing an end of said jacket and having .a;pair of lead-in wires projecting therethrough, av single upport rod fastened to one of said lead-in wiresand extending through the jacket, a pair of metal straps wrapped. around the pinch seals of the arc tube at pointsremoved from the ends of the arc chamber and fastened to said support rod, locking portions on said pinch seals inter-engaging the straps to prevent axial displacementof the arctube, and an inlead embedded in the pinchat ,the stem end of thearc tube providing a connection tothe. electrode and fastened to the other of said lead-in wires.

4. A lamp as in claim 3 wherein said locking portions consist of transverse ridges formed across the faces of the pinch seals.

5. A lamp as in claim 3 wherein said locking portions consist of funnel-like apertures formed in the ends of the pinch seals.

6. A lamp as in claim 3 wherein said locking portions consist of inter-engaging dents and bosses in the pinch seals and in the straps.

7. An electric discharge lamp comprising a vitreous outer jacket enclosing a generally cylindrical arc tube closed by full diameter pinch seals defining an arc chamber having electrodes sealed therein at opposite ends, a stem closing an end of said jacket and having a pair of lead-in wires projecting therethrough, a single support rod fastened to one of said lead-in wires and extending substantially the length of the jacket and provided wtih spring fingers at its outer end engaging the wall of the jacket to fix the rod in place, a connection from the electrode at the outer end of said are tube to said rod, a pair of metal straps wrapped around the pinch seals of the arc tube at points removed from the ends of the arc chamber and fastened to said support rod, locking portions on said pinch seals inter-engaging the straps to prevent axial displacement of the arc tube, and an inlead embedded in the pinch seal at the stem end of the arc tube and connected to the electrode thereat and fastened to the other of said lead-in wires to provide a current connection and mechanical support for said are tube.

8. An electric discharge lamp comprising a vitreous outer jacket enclosing a generally cylindrical arc tube closed by full diameter pinch seals defining an arc chamber, a stem closing an end of said jacket and having a pair of lead-in wires projecting therethrough, a single support rod fastened to one of said lead-in wires and extending substantially the length of the envelope and provided with spring fingers at its outer end engaging the wall of the jacket to fix the rod in place, a pair of metal straps wrapped around the seals of the arc tube at points removed from the ends of the arc chamber and fastened to said support rod, locking portions on said pinch seals inter-engaging said straps to prevent axial displacement of the arc tube, a main electrode at the outer end of said arc tube connected to said support rod, an auxiliary electrode at the stem end of said arc tube connected to said rod in series with a current limiting resistor, a main electrode at the stem end of said are tube provided with a foil seal through the pinch seal, and an inlead embedded in the pinch seal having a portion bent over at right angles and welded to the end of said foil and having another portion emerging from the seal through a funnel-like aperture near an edge thereof and fastened to the other of said lead-in wires.

References Cited in the file of this patent UNITED STATES PATENTS 1,948,261 Francis et al. Feb. 20, 1934 2,094,679 Schouwstra Oct. 5, 1937 2,830,210 Jenne et a1. Apr. 8, 1958 

